• Steel and Composite Structures
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• 제52권5호
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• pp.501-513
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• 2024

Two-directional functionally graded materials (2D-FGMs) show extraordinary physical properties which makes them ideal candidates for designing smart micro-switches. Pull-in instability is one of the most critical challenges in the design of electrostatically-actuated microswitches. The present research aims to bridge the gap in the static pull-in instability analysis of microswitches composed of 2D-FGM. Euler-Bernoulli beam theory with geometrical nonlinearity effect (i.e. von-Karman nonlinearity) in conjunction with the modified couple stress theory (MCST) are employed for mathematical formulation. The micro-switch is subjected to electrostatic actuation with fringing field effect and Casimir force. Hamilton's principle is utilized to derive the governing equations of the system and corresponding boundary conditions. Due to the extreme nonlinear coupling of the governing equations and boundary conditions as well as the existence of terms with variable coefficients, it was difficult to solve the obtained equations analytically. Therefore, differential quadrature method (DQM) is hired to discretize the obtained nonlinear coupled equations and non-classical boundary conditions. The result is a system of nonlinear coupled algebraic equations, which are solved via Newton-Raphson method. A parametric study is then implemented for clamped-clamped and cantilever switches to explore the static pull-in response of the system. The influences of the FG indexes in two directions, length scale parameter, and initial gap are discussed in detail.

• 한국공간구조학회논문집
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• 제12권3호
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• pp.79-87
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• 2012

본 연구에서 리드스위치를 이용한 정적변위센서를 무근과 철근 콘크리트 보에 부착하고 균열손상의 모니터링을 위해 무선주파수를 이용하였다. 무근 콘크리트 보와 철근 콘크리트 보에 외력이 작용하면 균열손상이 발생하고 균열의 증진으로 정적변위센서가 파괴되면 이와 연결되어 있는 무선주파수 발신자가 손상신호를 외부로 발신하게 된다. 이러한 기능성 건축부재에 대한 연구는 이상 기후 현상과 지진 등으로부터 건축물이나 주요구조물을 보호하는데 중요한 역할을 담당할 것으로 사료된다.

• 전력전자학회논문지
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• 제25권4호
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• pp.243-250
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• 2020

Energy harvesting is a recent technology involving the harvest and utilization of extremely small surrounding energy. Energy harvesting research is conducted in various fields. Triboelectric nanogenerators (TENGs) are energy harvesting technologies that use static electricity generated by physical movement or friction. Although TENGs generate output power in microwatt levels, they experience high internal impedance compared with other energy harvesting generators, thereby making the continuous transfer of electric power to loads difficult. This study proposes a power management system for TENGs that consists of three stages, that is, an AC/DC rectifier, an impedance coupler switch with a capacitor bank, and a DC/DC converter. In addition, the selection method of the AC/DC rectifier and DC/DC converter is proposed to maximize the amount of power transferred from energy harvesting areas. Furthermore, the impedance coupler switch and capacitor bank are discussed in detail. The validity and performance of the proposed three-stage power management system for TENGs are verified using a prototype system.

• Journal of Power Electronics
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• 제14권6호
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• pp.1243-1253
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• 2014

The phase inductance of a switch reluctance motor (SRM) is significantly nonlinear. With different saturation conditions, the phase inductance shape is clearly changed. This study focuses on the relationship between coefficient and current in an inductance model with ignored harmonics above the order of 3. A position estimation method based on the variable coefficient inductance model is proposed in this paper. A four-quadrant sensorless control system of the SRM drive is constructed based on the relationship between variable coefficient inductance and rotor position. The proposed algorithms are implemented in an experimental SRM test setup. Experimental results show that the proposed method estimates position accurately in operating two/four-quadrants. The entire system also has good static and dynamic performance.

• 전기전자학회논문지
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• 제10권2호통권19호
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• pp.149-155
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• 2006

In this study, the design of low voltage DC-DC converter with low triggering ESD (Electro-Static Discharge) protection circuit was investigated. The purpose of this paper is design optimization for low voltage(2.5V to 5.5V input range) DC-DC converter using CMOS switch. In CMOS switch environment, a dominant loss component is not switching loss but conduction loss at 1.2MHz switching frequency. In this study a constant frequency PWM converter with synchronous rectifier is used. And zener Triggered SCR device to protect the ESD phenomenon was designed. This structure reduces the trigger voltage by making the zener junction between the lateral PNP and base of lateral NPN in SCR structure. The triggering voltage was simulated to 8V.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2004년도 가을 학술발표논문집 Vol.31 No.2 (3)
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• pp.316-318
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• 2004

유선, 무선을 합하여 초고속 네트워크의 사용이 급격하게 증가됨에 따라 고속의 네트워크 통신 서비스에 대한 요구가 증가 하였으며 차별화된 인터넷 서비스에 대한 요구가 증가함에 따라 IP 기반의 스위치가 등장하게 되었다. 이러한 스위치의 이슈는 IT 포워딩, 고속 스위치 패브릭 등의 문제를 포함하게 된다. 현재까지의 모든 패킷 스위치는 그 내부적으로 HOL블로킹에 의한 성능 저하의 영향을 최소화하기 위하여 여러 가지 스케줄링 알고리즘을 사용한다. 본 논문에서는 Gigabit 으로 동작하는 패킷 스위치 중에서 Strict Priority 알고리즘, Round Robin 알고리즘을 분석하고 각각의 스케줄러가 COS 기반과 어떤 관계가 있으며 더불어 COS 기반에 따라, 스케줄러를 동적으로 변경하여 기존의 Static 하게 정책적으로 사용되던Algorithm 과의 차별성을 두어 동적 스케줄러의 선택에 의한 Packet 처리 성능향상을 보이도록 한다.

• Journal of Communications and Networks
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• 제5권1호
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• pp.82-89
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• 2003

In this paper, an efficient threshold-based filtering (TF) buffer management scheme is proposed. The TF is capable of minimizing the overall loss performance and improving the fairness of buffer usage in a shared buffer packet switch. The TF consists of two mechanisms. One mechanism is to classify the output ports as sctive or inactive by comparing their queue lengths with a dedicated buffer allocation factor. The other mechanism is to filter the arrival packets of inactive output ports when the total queue length exceeds a threshold value. A theoretical queuing model of TF is formulated and resolved for the overall packet loss probability. Computer simulations are used to compare the overall loss performance of TF, dynamic threshold (DT), static threshold (ST) and pushout (PO). We find that TF scheme is more robust against dynamic traffic variations than DT and ST. Also, although the over-all loss performance between TF and PO are close to each other, the implementation of TF is much simpler than the PO.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 전력전자학술대회 논문집
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• pp.654-656
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• 2001

This research used triac that is semi-conductor that act to static contact to overcome happened shortcoming been using mechanical centrifugal force switch usually Detect starting current of single phase induction motor and decided moving time. Therefore, could improve life of switch semipermanently. Also, wish to reduced impact that electric motor suffers at the starting moment and do stable starting which there is no life improvement and noise of electric motor itself, arc.

• Journal of Power Electronics
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• 제19권5호
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• pp.1133-1141
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• 2019

In this paper, a capacitors energy strategy based Cascaded H-bridge Converter (CHBC) for steady DC link voltage is proposed, which allow the CHBC to work while DC power fails. The topology of the CHBC is analyzed to construct the proposed strategy. The capacitors energy strategy is deduced based on the principle that the DC link voltage should be steady, the switch state should be smooth and the switch frequency should be normal. Experiments based on a three-module prototype, including static experiment, start experiment and step change experiment, proves the correctness of the strategy. They also verified the excellent fault tolerance ability and good dynamic performance of the proposed strategy.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1999년도 전력전자학술대회 논문집
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• pp.206-209
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• 1999

There exists an acute need for high voltage solid-state-switches in a broad area of applications. With the proposed method using simple voltage balancing circuit with series connected IGBTs, it is realized high voltage semiconductor switches with working voltages of several order kilo-volts. The operation principle of the proposed circuit is explained and analyzed. Transient and static voltage-balancing is tested on a experimenta 3kV/45A switch with four series-connected IGBTs.